In coating the enclosures of electric devices, spray guns are generally used to apply spray coating material dissolved in a volatile solvent to the enclosures of the electric devices. However, during coating, 60-70 percent of the coating material evaporates and only 30-40 percent of the coating material is adhered to the enclosures of the electric devices. The evaporating coating material needs to be dissolved in water, to avoid polluting the air.